"When 'foo' is used in connection with 'bar' it has generally traced
to the WWII-era Army slang acronym FUBAR [snip], later modified to
foobar. Early versions of the Jargon File interpreted this change as
a post-war bowdlerization, but it it now seems more likely that FUBAR
was itself a derivative of 'foo' perhaps influenced by German
furchtbar (terrible) -- 'foobar' may actually have been the original
form."

(That final "original" is in italics in the, um, original source.)

On Aug 24, 2006, at 1:23 PM, b. water wrote:

i did come across 'FUBAR' in 'Tango & Cash' but 'foo' on its own as
an acronym (or so i thought...) never.

From the same source:

"Several slang dictionaries aver that FOO probably came from Forward
Observation Officer, but this (like the contemporaneous "FUBAR") was
probably a backronym."

Note: I provide these only as reference; I cannot vouch for their
accuracy.